This invention relates to an engine cylinder block reinforcing structure in which the skirts on both sides of a cylinder block are connected at their lower ends by a reinforcing member to reinforce the cylinder block.
A known cylinder block reinforcing structure as disclosed in e.g. the specification of Japanese Utility Model Publication (KOKOKU) No. 55-40360 includes a reinforcing member (vibration-proof structure) attached to the lower end of the cylinder block together with an oil pan. In the cylinder block reinforcing structure, the skirts on both sides of the cylinder block are connected at their lower ends by the reinforcing member, whereby vibration of the skirts is suppressed. This serves to enhance durability and reduce vibration-induced noise. As set forth in the aforementioned specification, the reinforcing member comprises a frame-shaped member formed by forging or a metal plate material bent into a plate-shaped configuration by pressing.
A structure in which the rear side of the engine is shallowly formed is often employed as the oil pan attached to the lower end of the cylinder block. If the above-described reinforcing structure is applied to a cylinder block to which the oil pan having the aforementioned configuration is attached, interference between the oil pan and the reinforcing member on the rear side of the engine where the oil pan in shallowly formed cannot be avoided. This makes it necessary to dispose the reinforcing member at a portion of the lower ends of the skirts which exclude a predetermined range on the rear side of the engine. However, adopting such an arrangement results in a cantilever-type structure in which the lower ends of the skirts on both sides of the block are connected solely at their front sides. Consequently, the rear end of the reinforcing member serves as a fulcrum and vibration, particularly in the lateral direction, readily occurs at the portions of the skirts rearwardly of the fulcrum.
Furthermore, in the power plant wherein the transmission is connected to the engine, vertical vibration is a problem. In such case the point at which the engine and transmission are connected is the weakest in terms of strength, so that it is necessary to increase the rigidity of the connection with respect to bending or flexural vibration in the vertical direction.